Wave transmission



Jan. 14, 1930. 175. SHEAl ,743,691

WAVE' TRANSMISSION A Filed June 19. 1925 Patented `lari.. 14,1930

arrasar UNITED sf'ra'rssV PATENT ortica TIMOTHY E. SHEA, OF RUTI-IERFORD, `NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N.' Y., A CORPORATION OF NEW YORK WAVE TRANSMISSION Application led .Tune 19,

' This invention. relates to wave transmission, and particularly to selective circuits for separatingcarrier waves of different-v frequencies.l

An object of the invention 1s toimprove the selective transmission of the different channel frequencies in a` carrier signaling' In systems of this type, thenecessity of including a large number of channels within a somewhat limited overall frequency range makes it difficult to dsigndirectional filters because of the extremely large change in the transmission loss that is required in a relatively small frequency interval.

In order to prevent singing in two-way repeaters, the total loss in the loop circuit formed by the oppositely directed repeating channels must exceed the total gain of the amplifiers. Because of the difficulty in making the filter loss characteristics change rapidly enough to give a high loop loss, between their cut-off frequencies` however, singing may frequently occur within the repeater at a point between the upper and 0 lower transmission bands where the loss introduced by the filters is small. y

In accordance with the present invention, this difficulty is overcome by means of a tuned circuit inserted at the junction point of the directional filters and designed 'to 1925. Serial No. 38,134.

4resonate at some frequency in the region between Ithe .upper and lower transmission bands 1n the frequency scale. This added impedance is designed to add to the loss in this region without affecting the Iloss in the transmission bands 4of the filters.

The invention will -be described in con- .nection with the accompanying drawing in which:

-Fig. l is a diagrammatic illustration of a two-way repeater embodying the invention, in which the repeating channels are connected in series with the transmission line.

Fig. 2 shows a modification of the circuit of Fig. l, in which the repeating channels are connected in parallel with the transmission line.

Figs. 3 and 4 show curves illustrating the principle of operation of the repeaters of Figs. 1 and 2.

The two-'way repeater of Fig. 1 comprises two one-Way `repeating-channels RW and RE, adapted to -connect transmission line sections Wand E.

The currents incoming at the repeater from line section E are amplified in the channel and the amplified currents are delivered to line section W. Similarly7 the, currents incoming from line section W are amplified in the channel RW and the amplified currents are delivered to line section E.

The currents incoming from the line scction `W are of higher frequencies than thosey incoming from line section E. The respective repeater channels are provided vwith frequency discriminating filters which direct the incoming currents to the proper channels.

' The repeater channel RW includes a high pass input filter HPIF, an amplifying structure NVA, and a high pass output filter HPOF. The repeater channel RE vincludes a low pass input filter LPIF, an amplifying structure EA.;l and a low pass output filter nected in series with line section IV, while filters HPOF and -LPIF are similarly connected to line section E.

The amplifying structures WA and EA may be of any well-known type such, for example, as that disclosed in U. S. Patent No. 1,413,357 to P.' A. Raibourn, issued April i8, i922.

The directional filters HPIF and HPOF are designed to tiansmit currents of the upper group of frequencies assignedv to channel RiV, and to suppress from transmissioncurrents of lower frequencies, while the directional filters LPIF and LPOF are designed to transmit currents of the lower group of frequencies 'assigned to channel RE and to suppress currents of higher frequencies. These filters may be of the gen- -eral type disclosed in U. S. Patent No.

1,22(- ,113 to G. A. Campbell, issued May 22, 1917. r

In designing the high and low pass filters for channels RW and RE, respectively, it iS.

difficult to make the filter loss characteristics iise rapidly enough to give a high loop loss in the available frequency interval. This is shown graphically by the filter curves of Fig. 3, wherein the transmission loss of the filters is plotted against frequency.

The curves lip and lp represent the transmission loss characteristics of the high and low pass filters, respectively. The sum )t of the transmission losses of the high and low'pass filters forming the' repeater group, drops to a minimum between the transmissionbands of the filters, and may drop to such a low value as to permit singing within the repeater as a result of regeneration.

In order to increase the loss in this region, a loop timed circuit 1, comprising a low inductance and large capacity, is inserted in series with the filters HPIF and LPOFy of Fig. 1, a simi-lar timed circuit being inserted at the junction point of filters HP OF and LPIF. The added tuned circuits are identical and, as indicated by the resonance curve te of Fig. 4, are designed toresonate at some frequency in the region between the transmission bands of the high'and low pass filters. The sum of the transmission losses of the filters and the timed circuit causes a substantial total loss #Z in this region with-v In this case, a so-called stift` j shown in Figs. 1 and 2, #here two or more filters are connected either in series or in parallel to a common transmission line, it y is customary to terminate the filters at the -ends wliere they are joined together in a fractional termination designed to improve the loss characteristics ofthe filters, as disclosed in an application of O. J; Zobel,

Serial No. 377,965, filed' April 30, .1920,

which became Patent No. 1,557,230, -October Small reflection losses occurring near thel cut-off points of the filters due to the .presence of the tuned circuits illustrated in Figs. 1 and '2 may therefore be taken into consideration in determining the proper termination of the filters themselves.

The elements herein shown and described are considered as merely illustrative of the invention which, of course, is susceptible of various other modifications and adaptations.

What is claimed is:

1. A wave transmission system including a plurality of filters for transmitting mutually j exclusive bands of frequencies, and means comprising a' tuned circuit tol introduce a substantial transmission loss in the frequency region between said bands" of frequencies.

2. A wave transmission system-including a transmissionline, a plurality of filters connected in parallel circuit relation to said line for transmitting mutually exclusive bands of frequencies, and means to introduce a substantial transmission loss'inthe frequency region only between said bands of frequencies comprising an impedance element connected to said filters.

3. A wave transmission system including a transmission line, a plurality of filters connected to said line for tiansinissing mutually exclusive bands offrequencies, and a selective circuit directly connected to said filters to introduce a substantial loss at frequencies intermediate' said bands of frequencies.

4. A wave transmission system including a transmissionline, a pair of directional filters for transmitting mutually exclusive bands of frequencies associated with said line, and a tuned circuit inserted at the juno-- tion point of said filters and designed to resonate at some frequency` in the Aregion between .the upper and lower transmission Abands in the frequency scale.

5i In a two-way repeater for coupling two transmission llines over which the waves transmitted in one direction are of higher frequencies than those transmitted in the.

opposite direction, high and low pass filters for separating the directional frequencies,

and means comprising a tuned circuit for causing a substantial loop loss'in the frethe transmissron n quencyV region between bands of said lters.

6. In a two-way` repeater for., coupling two transmission lines over which the waves transmitted in one direction are of higher frequencies than those transmitted in the opposite direction, high and low pass filters for separating the `directional.frequencies, and a tuned rcircuit inserted at the junction point of said filters and designed to introduce a substantial loop loss in the'region between the transmission bands of said iilters. l A

l7. A wave transmission system comprising a transmission line over which the waves v.transmitted in one direction are of higher frequencies than those transmitted in the opposite direction, a repeater including high and low pass iilters connectedin series to said transmission line, and an impedance connected in series with said filters and adapted to introduce a substantial transmission loss in the frequency region between the transmission bands of said ilters.

In witness whereof, I hereunto subscribe my name this 16th day of June A. D., 1925.

TIMOTHY E. SHEA. 

